Memory provides data storage for electronic systems. Flash memory is one type of memory, and has numerous uses in modern computers and devices. For instance, modern personal computers may have BIOS stored on a flash memory chip. As another example, it is becoming increasingly common for computers and other devices to utilize flash memory in solid state drives to replace conventional hard drives. As yet another example, flash memory is popular in wireless electronic devices because it enables manufacturers to support new communication protocols as they become standardized, and to provide the ability to remotely upgrade the devices for enhanced features.
NAND may be a basic architecture of integrated flash memory. A NAND cell unit comprises at least one selecting device coupled in series to a serial combination of memory cells (with the serial combination commonly being referred to as a NAND string). NAND architecture may be configured to comprise vertically-stacked memory cells.
The vertically-stacked memory cells may be block-erased by generating hole carriers beneath them, and then utilizing an electric field to sweep the hole carriers upwardly along the memory cells.
A gating structure of a transistor may be utilized to provide gate-induced drain leakage (GIDL) which generates the holes utilized for block-erase of the memory cells. The transistor may be a select device, such as a source-side select (SGS) device. A channel material may extend along a string of memory cells and be gatedly coupled with the SGS device. The gatedly coupled portion of the channel is a portion that overlaps a gate of SGS device. It can be desired that such portion include both a heavily-doped lower region and a lightly-doped upper region; with both regions overlapping the gate of the SGS device. Specifically, overlap with the lightly-doped region provides a non-leaky “OFF” characteristic for the SGS device, and overlap with the heavily-doped region provides leaky GIDL characteristics for the SGS device. The terms “heavily-doped” and “lightly-doped” are utilized in relation to one another rather than relative to specific conventional meanings. Accordingly, a “heavily-doped” region is more heavily doped than an adjacent “lightly-doped” region, and may or may not comprise heavy doping in a conventional sense. Similarly, the “lightly-doped” region is less heavily doped than the adjacent “heavily-doped” region, and may or may not comprise light doping in a conventional sense. In some applications, the term “lightly-doped” refers to semiconductor material having less than or equal to about 1018 atoms/cm3 of dopant, and the term “heavily-doped” refers to semiconductor material having greater than or equal to about 1019 atoms/cm3 of dopant.
A select device may comprise any of numerous configurations, including, for example, a single MOSFET transistor, a one-wordline memory cell, a multi-wordline memory cell, etc.
The channel material may be initially doped to the lightly-doped level, and then the heavily-doped region may be formed by out-diffusion from an underlying doped semiconductor material. However, difficulties are encountered in utilizing the out-diffusion to obtain desired doping to a desired location within the gated region of the SGS device. Accordingly, it would be desirable to develop new integrated structures more suitable for achieving desired doping within the gated region of the SGS device, and to develop methods of forming such integrated structures.